Turbine nozzle construction



May 12, 1970 K. w. KARSTEN'SEN 3, ,5

' TURBINE NOZZLE CONSTRUCTION- Filed April 10, 1968 1 3 Sheets-Sheet 1INVENTOR KARL W. KARSTENSEN W wgni May 12, 1970 K. W. KARSTENSE NTURBINE NOZZLE CONSTRUCTION Filed April 10, 1968 3 Sheets-Sheet 2 Q uwmvINVENTOR KARL W. KARSTENSEN 9:4, ATTQRNEYS y 1970 K. w. KARSTENSEN3,511,577

TURBINE NOZZLE CONSTRUCTION Filed April 10, 1968 I 3 Sheets-Sheet 3 I Ef ""7 5 1 m (7/ l' S 1 Q S fl INVENTOR KARL W. KARSTENSEN United StatesPatent 3,511,577 TURBINE NOZZLE CONSTRUCTION Karl W. Karstensen, Peoria,Ill., assignor to Caterpillar Tractor, Co., Peoria, Ill., a corporationof California Filed Apr. 10, 1968, Ser. No. 720,148 Int. Cl. F01d 9/02US. Cl. 415137 4 Claims ABSTRACT OF THE DISCLOSURE A turbine nozzleconstruction having separately cast turbine vanes with machinedfootings. One footing is fastened in One shroud and the other footingradially floats in slots in the other shroud.

Present turbine nozzles in which the vanes are cast in one piece andrigidly connected to the inner and outer shrouds have proven to besusceptible to cracking due to thermal strain.

On the other hand, while fabricated nozzles avoid or appreciably reducesuch stress cracking problems, it is difiicult to keep the gas passagearea constant between the vanes of these nozzles due to castingvariations and the difficulty of jigging during brazing. These problemsresult in a loose fit of the cast surface in the shroud slots because ofclearance requirements. Also, use of these noules often produces unequalthermal growth during transient modes of engine operation. This resultsin undesirable nozzle and shroud support problems as well as turbinerotor tip clearance problems.

It is therefore an object of the present invention to provide a turbinenozzle in which the vanes are not susceptible to cracking due to thermalstrain.

It is also an object of the present invention to provide such a nozzlein which the gas passage area between vanes is constant.

It is also an object of the present invention to provide such a nozzlewherein gas leakage between the vane footings and the shrouds isminimized.

It is also an object of this invention to provide a nozzle having equalthermal growth in all vanes during transient modes of engine operation.

Another object of this invention is to provide an improved vane mountingconstruction for the nozzle vanes of an axial flow engine which allowsthe easy removal and replacement of individual vanes.

It is also an object of this invention to provide a turbine nozzlehaving a relatively cool and stable support casing which serves as acommon pilot for the turbine nozzle and rotor tip shrouds.

It is further object of the invention to provide such a nozzle havinglong flexible cylindrical elements supporting the shrouds so as tocontrol concentricity relative to the engine axis and reduce thermalstress at operating temperatures.

It is a further object of the invention to provide such a nozzle havingmachined slots in the shrouds so as to accurately position the vanes forcontrol of the exit area and to capture the vanes in correct radialposition.

It is a still further object of this invention to provide such a nozzlewherein the outer shroud has passages for delivering cooling air to thevanes while controlling thermal growth of the shrouds.

It is also an object of this invention to provide such a nozzle whereinthe inner shroud has passages for delivering cooling air to the vanesand controlling thermal growth of the shrouds.

Other objects of the invention will be apparent from the accompanyingdrawings and the following description.

Referring now to the drawings:

FIG. 1 shows a fragmentary sectional view of a gas turbine engineutilizing the instant invention;

FIG. .2 shows a cut-away portion of the nozzle of the present inventionwhich illustrates the manner utilized for capturing a vane in thenozzle;

FIG. 3 shows a view of the vane illustrated in FIG. 2 taken along a lineIIIIII in FIG. 2; and

FIG. 4 shows an alternate embodiment of that portion of the inventionutilized in capturing a vane in the nozzle.

In FIG. 1, there is generally illustrated a turbine 11, utilizing oneembodiment of the invention. The turbine contains a first stageexpansion system 13 and a second stage expansion system 15. Although theengine is illustrated as having two stages of expansion, it should berealized that a greater number of stages utilizing similar structure maybe installed, if desired. The subsequent description which will, ingeneral, be limited to the first stage 13, is applicable to allsucceeding stages with obvious differences in dimensions, displacement,etc.

As the gases enter stage 13, turbine guide vanes 17 direct the gases soas to provide a motive force against turbine blades 19. The vanes 17 arecast with integral footings 21 and 23 and each inner footing 23 iscamground to a specific profile positioned with respect to the vane airfoil. This will insure less variation in the gas passage areas even ifthere are casting variations.

The vanes will all be in the same position relative to their footingsafter machining. Each of the footings 21 fits within a slot 25 in theupper shroud 27 and the footings 23 fit within slots 29 in the innershroud 31. Slots 25 and 29 may be machined by any process which willinsure extremely close fit-as, for example, an electrochemical orelectro-discharged process. Footing 21 is radially positioned within theshroud 27 by a pair of flanges 33 and 35 which are held against shroud27 by a locking shroud 37. Footing 21 is axially positioned by a pair ofshoulders 39 and 41 in shroud 27. By machining shoulders 39 and 41 tocontrolled dimensional tolerances, each vane is caused to be properlyaxially positioned when it is inserted into its slot 25.

Footing 23 is allowed to float radially in slipfit cooperation with slot29 in shroud 31.

Outer shroud 27 and locking shroud 37 are suitably fixed as by weldingto cylindrical support members 45 and 47, respectively. Support members45 and 47 are, in turn, suitably attached to bolt flanges 49 and 51,respectively, and the flanges are fastened to housing 53 of the turbineby a series of bolts 55.

When the engine is in operation, each shroud will tend to expand indirect relation to its proximity to the combustion chamber and thevanes. In other words, the outer shroud and the locking shroud will tendto expand to a greater extent near blades 17 and outer footings 21 thanat the outer edge of their conical supporting sections. In turn, thosesections -will tend to expand to a greater extent than their respectivesupport members 45 and 47. Due to the rigidity of such a turbine nozzlestructure, this relative expansion will cause the conical supportingsections to assume a slightly greater degree of taper when the engine isin operation than when cold and the conical support members 45 and 47,being of very thin cross-section, will take on a very shallow S-shapedwave (in longitudinal cross-section) extending throughout the greaterpart of their lengths and completely around the circumferences thereof.Thus, a high degree of flexibility is provided so as to avoid crackingdue to thermal stress, while maintaining the individually replacablevanes in an axially fixed position.

Referring to FIG. 1, it is seen that the stator and rotor shrouds of thesecond expansion stage are fixed similarly to those of the first stage.Since the second stage cylindrical support members are shorter thanthose in the first stage, less expansion take-up will occur in them, butsince the structure is necessarily cooler in the second stage, due tothe lowering of the gas temperature by its expansion, less expansionwill occur and the results will continue to be satisfactory. This willalso hold true if additional expansion stages are stacked in the mannershown.

In assembling the engine, the nozzles are installed in a stacked manneralternating with the rotors and, as previously stated, as many expansionstages desired may be so stacked. Bolt flanges 49 and 51 of the firststage shrouds are fitted against housing 53 and a labyrinth seal,generally shown at 61, is installed and held in place by bolts 63. Afirst stage rotor 65 carrying turbine blades 19 is then stacked upon adrive flange 67 by means of a Curvic coupling 69. The bolt flanges ofthe shrouds of the second stage and any succeeding stages are thenassembled against flanges 49 and 51 and bolts 55 are inserted throughhousing 53 to hold the flanges against the housing. A second labyrinthseal indicated generally at 71 is then installed and a second stagerotor 73 is stacked on the first stage rotor by means of a second Curviccoupling 75.

A series of other well known parts (not shown) are then stacked againstthe rotors and a flange (also not shown) and tie bolt 77 secure them inplace.

If it is desired to cool the vanes, air may be forced through aplurality of passages 79 in housing 53 to a corresponding set ofpassages 81 in the respective bolt flanges. This air will be forced intochambers 83 and 85. The air in chamber 83 is then passed through holes84 in the locking shroud and holes 87 in vanes 17, through the innershroud, and into the inner edge of the gas flow path on blades 19. Theair in chamber 85 will pass between shroud 27 of the first stage and theouter shroud of the second stage and enter the gas flow path at theouter edge of the path.

Referring now to FIG. 4, there is shown an alternate embodiment of thestator vane holding structure wherein vanes 117, utilized to direct thegases against the rotor blades 119, have outer footings 121 and innerfootings 123. An upper shroud 127 having machined slots 125 allows thefooting 121 of each vane to float radially in slip fit cooperation withthe slot. Inner footing 123 is fixed, as by brazing, within a slot 129in the inner shroud 131.

Cooling air can enter the nozzleflarea in a different manner than thatdescribed relative to the first embodiment, if desired. A passage 150just forward of the plenum wall 152 transfers air through openings 154and 156 in the plenum wall and lower shroud respectively. It is thendirected upwardly through passages 187 in the vane, through chamber 158and opening 160 and into the outer edge of the gas flow. If necessary,it can also enter the inner edge of the flow via holes 162 in the innershroud.

This embodiment could, if desired, be mounted within a turbine in thesame fashion shown in the embodiment described relative to FIGS. 1 and2. In order to enable the reader to more clearly understand how thiswould be accomplished, it is pointed out, whenever possible, thatidentical identification labels have been utilized in both embodiments,except that the labels in the embodiment 4 of FIG. 4 are preceded by thenumeral 1, so that, in. example, vane 17 becomes vane 117, etc.

Thus application has provided a relatively cool and stable supportcasing acting as a pilot for both the rotor and the nozzle tip shroudswhich shrouds comprise long, flexible cylindrical elements controllingthe vane concentricity with the engine axis, even when operatingtemperatures create thermal stress. Changes in structure and dimensionof the illustrated embodiments of the invention may be made withoutexceeding the purview of the following claims.

What is claimed is:

1. In a turbine stator an inner shroud fixed within the turbine housingand having at least one aperture therein for receiving a stator vanefooting,

an outer shroud fixed within the turbine housing in radial spacing fromsaid inner shroud and having at least one aperture therein for receivinga stator vane footing,

a recessed section in one face of one of said shrouds about said atleast one aperture therein,

a locking shroud fixed within the turbine in relatively close radialspacing from one of said shrouds, and

at least one vane extending between said inner and outer shrouds andhaving an inner footing slidably received in said at least one aperturein said inner shroud,

an outer footing slidably received in said at least one :aperture insaid outer shroud, and

a flange means on said vane and extending about one of said footings,slidably received within said recessed section in said one of saidshrouds, and closely adjacent said locking shroud such that said vane isheld in place by said locking shroud.

2. The turbine stator of claim 1 including means for removably attachingsaid locking shroud and said closely spaced shroud to a turbine housingat a single point in the housing.

3. The turbine stator of claim 2 including thin flexible members betweensaid locking shroud and the housing and between said closely spacedshroud and said housing.

4. The turbine stator of claim 1 wherein said closely spaced shroud issaid outer shroud and said locking shroud is radially outward thereof.

References Cited UNITED STATES PATENTS 2,937,000 5/ 1960 Ledwith.

2,984,454 5/ 1961 Fiori.

3,043,564 7/ 1962 Small.

3,062,499 11/ 1962 Peterson.

3,075,744 1 1963 Peterson.

3,295,824 1/ 1967 Woodwell et al.

3,314,648 4/ 1967 Howald.

FOREIGN PATENTS 626,818 7/ 1949 Great Britain.

EVERETTE A. POWEL In, Primary Examiner

